Polyols are attractive as sugar substitutes in food contexts because of their metabolic, dental and technical characteristics. Among the polyols maltitol, xylitol and lactitol have gained wide acceptance in various applications in the food and pharmaceutical industry.
Maltitol is a polyol which is commercially produced by the hydrogenation of maltose. Maltitol has a sweetness, which is about 85 to 95% that of sucrose and it exhibits a weak cooling effect when dissolving in the mouth. Maltitol is non-cariogenic and non-insulin-dependent which promotes its use as a sugar substitute in confectionery and dietetic foods.
Maltitol has a melting point of 148-151° C. and a solubility of 62% (w/w) in water at 20° C. and it was for a long time available only as a syrup since it was difficult to crystallize and since spray drying of maltitol produces a sticky hygroscopic powder which adheres to the walls of the equipment. The prior art indicates that no method for the crystallization of maltitol from impure solutions is known and that even the crystallization of pure maltitol is slow and complicated.
Thus, EP 0 491 953 describes a method for the crystallization of maltitol by feeding a maltitol solution to an extruder, adding maltitol seed crystals, cooling and kneading and then extruding the resulting magma through a nozzle. According to the patent, spray drying of maltitol is problematic since maltitol tends to form supersaturated solutions and has a low rate of crystallization. Spray drying resulted in sticky and glassy products which were not satisfactory.
In US JP 9110891 the problems with spray drying of maltitol were solved by first causing precrystallization of maltitol in an aqueous maltitol solution having a maltitol purity of 85-99.9% by weight during 5 to 30 hours to provide a massecuite of maltitol containing up to 50% suspended crystals and then spraying the massecuite into drying air. The resulting product was aged for 10 hours and then additionally dried.
In U.S. Pat. No. 4,408,041 and its divisional patent U.S. Pat. No. 4,717,765 seed crystals of maltitol having a purity of 99.8% were added to an 80% maltitol solution to provide a mascuite which was then spray dried, fluidized and aged to provide a crystalline product.
In U.S. Pat. No. 5,873,943 a maltitol syrup having a purity of 92 to 99.9% was condensed, crystallized to provide seed crystals and spray dried to provide a solid containing crystalline maltitol.
Finally, U.S. Pat. No. 5,651,829 describes a process whereby the crystallization of maltitol in an atomizing apparatus is made possible, but only provided that very specific process conditions are met. Thus, the maltitol concentration of the maltitol syrup must be at least 92%, the syrup must be sprayed onto a moving pulverulent bed having a similar maltitol concentration and having a mass which is at least twice that of the syrup. The resulting product comprises crystalline maltitol microparticles agglomerated with each other.
Xylitol is commercially produced from xylan obtainable from various vegetable sources. It is the sweetest of the polyols and is extensively used in confectionery, dietetic foods, oral hygiene products and in pharmaceuticals. It is not only non-cariogenic but also exhibits anti-cariogenic properties, which makes its use, for instance in tooth paste, hard candy and chewing gum very desirable. Xylitol provides a pronounced cooling effect when it dissolves in the mouth and this is appreciated in many applications.
Xylitol has a solubility of 63 (w/w) in water at 20° C. and it crystallizes from aqueous solutions into crystals melting at 92 to 96° C. Crystalline xylitol exhibits a higher hygroscopicity than maltitol and in solution it has a lower viscosity than maltitol at the same concentration.
Crystalline xylitol is conventionally produced by crystallization from aqueous solutions. Crystallization of xylitol from aqueous solutions requires a high xylitol purity of the solution in order to provide acceptable crystals (see U.S. Pat. No. 4,066,711). Thus, complex chromatographic methods have been employed for providing a sufficient purity of the solution. Xylitol has also been melt crystallized from substantially water-free melts as described in JP 7416929 and subsequently also in U.S. Pat. No. 5,139,795. The obtained crystals may be milled to a powder before use.
Xylitol has also been produced in microcrystalline form as described in WO 99/59426 by contacting a xylitol solution with gas suspended solid xylitol particles, allowing microcrystallization to proceed and recovering a porous agglomerated microcrystalline xylitol product.
Lactitol is a polyol with a mild sweetening capacity and a low cooling effect compared to xylitol. In recent years lactitol has gained wide acceptance in confectionery, dietetic foods and pharmaceuticals such as in chocolates and mild laxative preparations.
Lactitol was for a long time considered impossible to crystallize properly. This is partly due to the great variety of lactitol forms which may crystallize out of an aqueous solution. Thus, there exist at least two anhydrous forms of lactitol melting at 121-123° C. and 146-152° C., respectively, at least one monohydrate melting at 90-100° C., at least one dihydrate melting at 72-75° C. and at least one trihydrate melting at 38-45° C. Lactitol is further capable of crystallizing in a variety of random lactitol-water structures and it also solidifies in amorphous form. Crystallization of lactitol from an aqueous solution requires a high lactitol purity of the solution in order to provide a stable crystalline product. The specific conditions for crystallizing each one type of lactitol in pure form are known today and are described in WO 98/39350.
Lactitol has also been produced in microcrystalline form as described in WO 99/47532. Reference is also made to EP 832 899.
In the prior art there are also disclosed some polyol products containing one or more of the present polyols, maltitol, xylitol and/or lactitol.
U.S. Pat. No. 5,017,400 describes a physical combination of milled crystalline xylitol and maltitol to provide a sweetener mixture with improved taste properties.
FR 2786665 describes a hard fondant containing vegetable oil or fat and a mixture comprising maltitol and xylitol.
U.S. Pat. No. 5,045,340 describes a hard confectionery containing xylitol and maltitol or lactitol. The sweets are produced by melting a mixture of xylitol and maltitol or lactitol and adding powdered xylitol to the cooled mixture under agitation.
U.S. Pat. No. 6,165,511 describes a polyol composition obtained by co-spray drying of at least two polyols. The process requires that at least 80% by weight of the product is a non-hygroscopic polyol, which according to the examples is always mannitol. Mannitol is known for its very low hygroscopicity and extremely low solubility and therefore it is easy to spray dry.
U.S. Pat. No. 5,958,471 describes a polyol composition obtained by co-spraydrying a mixture consisting essentially of sorbitol, xylitol and mannitol dissolved in water. The content of sorbitol in the mixture is 70 to 98%.
U.S. Pat. No. 5,376,389 describes a dual coating of xylitol and another polyol wherein the polyols are sprayed as sequential layers on the surface of chewing gum pellets. The dual coating is said to provide improved coating quality compared to a conventional xylitol coating.
WO 99/18935 describes a directly moldable tabletting aid containing more than 90% by weight of xylitol and less than 10% of another polyol. The tabletting aid is obtained by co-spraydrying or co-granulation of the polyols.
U.S. Pat. No. 5,580,601 describes a grainy confectionery product containing maltitol or xylitol in crystalline form. Small powdered crystals of the respective polyol are mixed into a cooked mass of solubilized polyol to provide a soft and grainy sweet with a water content of 3 to 20%.
Although the prior art includes a vast number of documents describing the crystallization of the present polyols on their own, and even some documents in which mixtures of polyols are provided, it is evident that especially the crystallization of xylitol, maltitol and lactitol poses special problems which makes crystallization complicated.
The polyols have a high solubility and the products produced by spray drying especially of solutions containing impurities have been sticky and instable. A typical example of this can be found in the spray drying of maltitol, where the prior art requires a maltitol concentration of above 92% (U.S. Pat. No. 5,651,829) in order to avoid undue stickiness and to obtain a satisfactory crystal by fluidizing. Stickiness is typically also due to enclosed water and amorphous products, both problems being well known from the crystallization of maltitol and lactitol.
Maltitol, xylitol and lactitol all require very high purity of their aqueous solutions for satisfactory conventional crystallization. Imperfectly crystallized polyols tend to be hygroscopic, which easily leads to instability during storage. It has not been possible to satisfactorily crystallize the individual polyols from aqueous solutions containing impurities, such as other polyols, in amounts as high as 25%.
Thus, combinations of the polyols have generally been made by physically mixing pure crystals of the separate polyols.
However, in the context of the present invention it has surprisingly been found that the polyols do not require the same purity for satisfactory microcrystallization according to the present invention. The present microcrystalline polyol compositions are obtained from solutions having a very high amount of “impurities”, i.e. from solutions containing at least 25% of another polyol.
The polyols useful for providing the polyol composition of the present invention may naturally be purified individually before being used in the preparation of a liquid feed polyol mixture. However, it is one of the advantages of the present invention that such purification is not necessary and that crude polyol mixtures may be used as the starting material.
An object of the invention is to provide a product which avoids the drawbacks of the prior art and which provides a non-cariogenic polyol composition of maltitol, xylitol and/or lactitol in an intimately mixed ready-to-use form.
It is an object of the invention also to provide a stable and homogeneous pre-mixture of two or more polyols which mixture has a desired content of each of the polyols in the mixture and wherein there is no separation and/or fractionation of the polyols within the composition itself.
It is an object also to provide a stable polyol composition which is substantially non-hygroscopic and free-flowing.
It is an object of the present invention to develop a polyol composition having the desired sweetening capacity, cooling effect, laxative effect, non-cariogenic or anti-cariogenic effect etc., in other words, a composition having the desired properties of each of the polyols in the composition. By including the polyols in one and the same composition it is possible to avoid the need for separate mixing of the various component polyols at the point of use. The intimately mixed polyols in the homogeneous composition are not subject to separation and/or segregation.
An object of the invention is also to provide a novel granular polyol composition which is suitable for use in the confectionery as well as in the food and pharmaceutical industry. An object of the present invention is also to provide an improved process for the crystallization of polyol composition(s).
Another object of the present invention is to provide a particulate polyol composition product in a process which transforms a polyol solution into a solid polyol composition product in one overall operation.
An object is also to provide a process having a fast over-all operation. The process provides crystallization of the polyol solution in a significantly shorter time than conventional crystallization. Thus, the present microcrystallization process lasts only seconds in the air while a standard aqueous crystallization lasts for hours, mostly tenths of hours.
An advantage of the present invention is that it provides a non-cariogenic sweetening composition wherein maltitol and/or lactitol benefit from the anti-cariogenic properties and higher sweetness of xylitol.
A further advantage of the invention is that it provides a non-cariogenic sweetening composition wherein the pronounced cooling effect of xylitol, which is, for instance not desired in chocolates, is reduced by maltitol and/or lactitol.
An advantage is also that it provides a non-cariogenic sweetening composition wherein the burning aftertaste, which is felt in some cases when xylitol is used as the sole sweetener, is reduced by maltitol and/or lactitol.